O Radical‐Induced n‐to‐p Transition in PbS Quantum Dots Enabling Enhanced and Stable Photogating in QD/IGZO SWIR Phototransistors

ABSTRACT

Colloidal PbS quantum dots (QDs) are promising photosensitizers for short‐wave infrared phototransistors. But their photogating efficiency is limited by unfavorable energy band alignment and interfacial defects. Here, we report an O radical exposure to induce an effective n‐to‐p transition in PbS QDs using atmospheric Ar/O ₂ plasma (AAP). This leads to enhanced and stable photogating effect in PbS QD/IGZO phototransistors. Ultraviolet photoelectron spectroscopy (UPS) results show the work‑function increase from 4.10 to 4.47 eV and the shift of E _F toward mid‑gap, E _C ⁻ E _F shifts from 0.26 to 0.65 eV by 15 cycles of AAP treatment. The XPS results indicate the increase of M─O from 44.9% to 81.1%, and the decrease in oxygen vacancies (V _O ) from 38.8% to 16.1%, and hydroxyl (─OH) concentration from 16.3% to 2.8% at the interface by AAP. These modifications suppress off‐state current (I _off ), shift threshold voltage (V _TH ) to positive, minimize interface trap density (D _it ), and suppress photocurrent decay, thereby stabilizing photogating effect. The AAP‐treated device shows the responsivity 2883 A W ^{− 1} , detectivity 7.43 × 10 ^{1 3} Jones, and EQE 2.75 × 10 ⁵ % at 1300 nm under 1 mW cm ⁻² . A 5 × 5 pattern recognition array based on PbS QD/IGZO phototransistors shows alphanumeric patterns under SWIR illumination.